1. Field of the Invention
The present invention relates to the field of electronic pressure scanners developed to withstand the extreme environmental conditions associated with the design and development of modern gas turbines.
2. Discussion of Background
Because of the need to perform many measurements, the design and the development of modern gas turbines is a complex and expensive operation. Testing turbines require mostly low frequency air pressure measurements in order to assess the turbine steady state performance and a fewer number of measurements in the 100 Hz region to analyze the turbines handling characteristics. The low frequency measurements may require up to 2000 parameters to be measured and with up to 500 parameters required to be measured in the 100 Hz region. In order to reduce pneumatic delay and increase throughput, there is a requirement for the transducers and the signal conditioning equipment associated with them to be moved from the control room to the engine test frame or to the vehicle. Thus, because of the relocation of the instruments from the control room to the engine test environment, there must be a strict immunity to temperature extremes and to vibrations while the same accuracy must be found in the engine environment as had been obtained in the control room environment.
The prior art electrically scanned pressure sensor modules which utilize pressure sensor chips are exemplified by U.S. Pat. No. 4,111,058 wherein a plurality of solid state pressure sensor chips and signal multiplexing electronics are integrally mounted on a position pressure selector switch which has a plurality of positions. A first position of the switch connects a calibrating pressure source to all of the pressure sensor chips. The other positions of the selector switch provides for connections with the plurality of different locations which are connected to the chips. A digital code is applied to the multiplexing electronics during the time that the pressure selector switch is at each of its multiple positions. The analog output of all the sensors is multiplexed into a single output to reduce the number of wires which exit the instrument.
Despite the theoretical applicability of this type of system, it can be seen that the use of the pneumatic switching structure inherently provides delays required by the switching time which severely limits the scanning rate which can be accomplished. Furthermore, the structure of this type of system inherently precludes any field repair due to an inevitable break down of any one of the sixteen transducers. Not only is it impossible to determine what has failed about the transducer, but it is impossible to replace an individual transducer in the field.
Other problems which exist with this type of prior art shown by U.S. Pat. No. 4,111,058 include a lack of an option for individual differential configurations, the ability to select calibration and measurement reference pressures and any reliability during its operation in high vibration applications. It is also notable that this type of prior art scanner is not able to distinguish between the various transducers in the sense that there is no assurance that each transducer is compensated with respect to zero offset and thermo-zero shift in any manner different from any of the other sixteen transducers. This inherently limits the accuracy available at the outputs.
It is this type of system to which Applicant's present improved invention is addressed.